The preparation of siloxane-oxyalkylene copolymers by the hydrosilation reaction of an organohydrogensiloxane and an olefinically substituted polyoxyalkylene is well known and reported in the literature. The hydrosilation reaction is typically performed in a low molecular weight volatile hydrocarbon solvent such as benzene, toluene, xylene or isopropanol so as to aid in handling the reactants, to moderate an exothermic reaction or to promote the solubility of the reactants.
Prior to the present invention there were few literature references to a solventless process for the preparation of siloxane-oxyalkylene copolymers. For example, in U.S. Pat. No. 4,025,456, it was indicated that the hydrosilation reaction between the organohydrogenpolysiloxane reactant and the olefinically substituted polyoxyalkylene reactant may be conducted without a solvent or conducted in an oxygen containing solvent such as an ether, a polyether, or a lower or higher molecular weight alcohol. This reference, however, utilized alkoxy endblocked polyethers in the hydrosilation reaction and did not disclose the use of uncapped oxyalkylene polyethers.
In most cases, however, the prior art discloses the use of one or more solvents. Thus, for examples, U.S. Pat. No. 4,520,160 teaches the use of high molecular weight, 8-carbon fatty alcohols for the preparation of siloxane-oxyalkylene copolymers. The patent indicates that isopropanol is used as a solvent and must be removed from the product while the fatty alcohol constitutes a part of the product.
Other references, such as, U.S. Pat. Nos. 3,280,160 and 3,401,192 disclose the preparation of copolymers in n-butylether and in a 50/50 mixture of isopropyl alcohol/toluene, respectively. Also in U.S. Pat. No. 4,122,029 the use of isopropyl alcohol is disclosed and in U.S. Pat. No. 3,518,288 the patentee teaches the use of n-propanol/toluene as a suitable solvent for the preparation of siloxaneoxyalkylene copolymers.
In the majority of the aforementioned processes, the hydrocarbon solvent is removed after the hydrosilation reaction is completed, since in most cases, the solvent is too flammable, toxic or otherwise detrimental to the final product or further processing steps in which the copolymer is utilized. Thus, in the processes disclosed in most of the above patents a solvent was employed which required removal from the reaction product after completion of the hydrosilation.
A few instances have been reported in the literature where for one reason or another it was not necessary nor desirable to separate the copolymer from the reaction medium. For example, U.S. Pat. No. 4,520,160 disclosed the use of saturated higher alcohols as a reaction solvent which purposely need not be removed from the resulting copolymer when it is used subsequently in personal care compositions as emulsifiers.
In many instances, however, the solvent does not enter into any further reactions but remains in the final product as is, and hence, there is no need for its removal if it does not adversely affect the product. Thus, in some products, such as personal care products it may even be benefical to have some of the solvent present in the final product.
However, if the copolymer is to undergo further reactions before preparation of the final product is complete, the presence of the solvent might adversely affect such reactions and hence its removal after the hydrosilation step is desired. For example, if one were to use copolymers containing monohydric higher alcohols in urethane foam applications, these alcohols will enter into the urethane reaction and act as reaction chain terminators in a detrimental fashion since they contain only one hydroxyl group. Also, as previously indicated, such solvents may be toxic or otherwise undesirable in further processing of the copolymer. Accordingly, any process which could effect the hydrosiliation reaction in the absence of a solvent would be highly desirable not only from the economic viewpoint in the savings obtained by avoiding a solvent removal step, but also for environmental considerations.
Thus, prior to the present invention, no mention was made in the literature to a solventless process for the preparation of siloxane-oxyalkylene copolymers from uncapped polyethers. The majority of the known processes, as indicated above, utilize a solvent.
Additionally, there are few references in the literature to the use of acid or acid salts in the hydrosilation reaction. U.S. Pat. No. 4,431,789 which is assigned to Shin-Etsu Chemical Co., describes the use of potassium acetate salt with very high (&gt;50%) solvent (isopropanol) levels for the preparation of organopolysiloxanes having alcoholic hydroxy groups. Finally, U.S. Pat. No. 4,515,979 discloses the addition of phytic acid to the polyether but the use of the acid is for the prevention of odors in polyorganosiloxanes.
It is therefore an object of the present invention to provide an improved process for the preparation of siloxane-oxyalkylene copolymers. Another object of this invention is to provide a process for the preparation of siloxane-oxyalkylene copolymers which are useful in the formulation of urethane foams and wherein the hydrosilation reaction is conducted using little or no solvent. A further object of the present invention is to provide a novel process for preparing siloxane-oxyalkylene copolymers from uncapped, generally oxyethylene-rich polyethers, in the absence of solvent. A further object of the invention is to provide a process which utilized a carboxylic acid or a carboxylic acid salt as a catalyst modifier to be added to the reaction mixture for the hydrosiliation reaction. A still further object is to provide a process wherein the use of the acid or salt prevents gelation and also prevents acetal formation through stabilization of propenyl groups. Another object is to provide a process having improved batch production rates of a factor of three or four by eliminating the solvent-stripping and acetal cleavage steps. Another object of this invention is to provide a process which provides improvement in product safety and reduction in solvent emission. A further object of the invention is to provide a process for the preparation of urethane foams which have improved flow properties and other desirable features. These and other objects will readily become apparent to those skilled in the art in the light of the teachings herein set forth.